1. Field of the Invention
The present invention relates to a fuel injection apparatus and applied to a diesel engine, etc. equipped with an accumulator fuel injection apparatus, the apparatus being composed such that; high pressure fuel pumps are provided each of which compresses fuel introduced into its plunger room to high pressure by its plunger fitted in its plunger barrel and reciprocated by means of a fuel cam to supply the compressed fuel to a common rail, and high pressure fuel accumulated in the common rail is injected periodically at determined injection timing into each of the cylinders of the engine, and a method of operating the engine equipped with the apparatus.
2. Description of the Related Art
An accumulator fuel injection equipment used in a diesel engine is provided with high pressure fuel injection pumps each of which compresses fuel introduced into its plunger room to high pressure by its plunger fitted in its plunger barrel and reciprocated by means of a fuel cam, and high pressure fuel accumulated in the common rail is supplied to each of fuel injection valves to be injected periodically at determined injection timing into each engine cylinder.
In an accumulator fuel injection apparatus like this, discharge duration of high pressure fuel from each of the high pressure pumps is controlled by controlling opening/closing of a low pressure side fuel feed passage by means of an electromagnetic valve provided to each pump as disclosed for example in Japanese Laid-Open Patent Application No. 64-73166 (patent literature 1) and Japanese Laid-Open Patent Application No. 62-258160 (patent literature 2).
FIG. 2B represents a diagram showing a fuel cam lift and opening/closing of the electromagnetic valve vs. crankshaft rotation angles in the electronically-controlled accumulator fuel injection apparatus disclosed in the patent literature 1.
As shown in FIG. 2B, in the conventional electronic control accumulator fuel injection apparatus, the electromagnetic valve is closed on the way the cam lift is increasing to begin fuel discharge from the high pressure fuel pump, and opened when the cam lift is at its maximum to allow high pressure fuel remaining in the plunger room (volume of the plunger room is at minimum, i.e. dead volume) of the high pressure pump to spill out to the fuel feed line (low pressure side fuel line).
FIG. 5 is a drawing for explaining working of a high pressure fuel pump 020 in the conventional accumulator fuel injection apparatus. In the drawing, change of lift of fuel cam 04, open or close of inlet/spill port 010a, and direction of fuel flow at inlet/spill port 010a are shown as the fuel cam 04 is rotated.
In FIG. 5, at (A) (crankshaft rotation angle θ=θ0=0°), the plunger 02 is at its bottom dead center (at zero lift of the fuel cam 04), the top end of the plunger 02 has fully opened the port 010a, and fuel fed from the fuel feed line has been introduced into the plunger room 03.
At (B) (crankshaft rotation angle θ=θ1), the plunger 02 has moved up until a position where the top end of the plunger 02 fully closes the port 010a, and pressure feeding of fuel to the common rail begins. The fuel fed to the common rail is accumulated therein.
At (C) (crankshaft rotation angle θ=θ21 and is before the top dead center of cam lift), the plunger 02 has moved up until a position where the leading edge 02a of the spill groove of the plunger 02 just begins to open the port 010a, and fuel in the plunger room 03 begins to spill out to the port 010a. 
At (D) (crankshaft rotation angle θ=θ22), the plunger 02 has passed over the top dead center and moved down until a position where the leading edge 02a of the spill groove of the plunger 02 fully closes the port 010a, and fuel spilling from the port 010a ceases.
At (E) (crankshaft rotation angle θ=θ3), the plunger 02 has moved down until a position where the top end of the plunger 02 begins to open the port 010a, and fuel begins to enter the plunger room 03.
At (F) (crankshaft rotation angle θ=θ0), the plunger 02 is again at the bottom dead center of cam lift, and the port 010a is fully opened by the top end of the plunger 02.
In prior art disclosed in the patent literature 1, the electromagnetic valve is closed on the way the cam lift is increasing to begin fuel discharge from the high pressure fuel pump, and opened when the cam lift is at its maximum to allow high pressure fuel remaining in the plunger room to spill to the fuel feed line.
Therefore, when the electromagnetic valve is opened at the top of the fuel cam lift, high pressure fuel remaining in the plunger room spills out from the plunger room to the fuel feed/spill passage of low pressure at high speed as shown in FIG. 2B.
In prior art disclosed in the patent literature 2, also high pressure fuel spilling occurs.
In an accumulation fuel injection apparatus of prior art in which the plunger has a spill groove, also spilling of high pressure fuel remaining in the plunger room occurs when the fuel inlet/spill port 010a is opened by the leading edge of the spill groove of the plunger, and high pressure fuel spills out rapidly at high speed through the inlet/spill port to the feed/spill passage as shown in FIG. 5.